The relationship between phosphorus and carbon chemistry has been realized for many years. Phosphorus relatives of classical organic ligands (like cyclopentadienide, Cp^–) in which carbon atoms have been substituted for phosphorus atoms are important classes of organometallic ligands, which are relevant to catalysis. Often, however, a limit to applying the phosphorus counterparts is the low-yielding and circuitous nature of their synthesis. A case in point is the 1,2-diphospholide ligand framework, an important analogue of the cyclopentadienyl ligand, which has only been obtained from multistep syntheses. We report in this paper a high-yielding and direct route to this type of framework using a very simple approach. Treatment of MesPHLi (Mes = 2,4,6-trimethylphenyl) with Sb(NMe₂)₃ generates the 5,7-dimethyl-1,2-benzodiphosphol-1-ide anion (1), the first 1,2-diphospholide analogue of indenyl. Structural and NMR spectroscopic investigations suggest that this unique reaction, involving double C–H deprotonation of a CH₃ group of the Mes ligand, occurs through the rearrangement of a tetraphospha-1,4-diide anion.

Attempted synthesis of the ylide dianion [2,4,6-Me₃C₆H₂P(CHR)₃]^2– (2,4,6-Me₃C₆H₂ = mesityl, R = H or Me) by the reaction of mesitylphosphonium iodides [2,4,6-Me₃C₆H₂PR₃]⁺I^– (R = Me, 1; R = Et, 2) with tBuLi at reflux does not result in the anticipated deprotonation of the phosphorus-bonded R groups. Instead, quantitative 1,3-sigmatropic rearrangement occurs to give new benzylic phosphonium salts [(3,5-Me₂C₆H₃)CH₂PR₃]⁺I^– (R = Me, 6; R = Et, 7), in which the phosphonium centre, the R₃P group, is transferred to an ortho-CH₃ group. In situ ³¹P NMR spectroscopic studies show that the reaction is base-activated and stoichiometric with respect to tBuLi. DFT calculations support the conclusion that the rearrangement is thermodynamically favourable in the gas phase and in THF and show that the rearrangement is enthalpically driven.

A series of group 1 metal salts of the pentacyanocyclopentadienide anion [Cp(CN)₅^–] (1) have been crystallised from two distinct solvent systems and the structures of the resulting species investigated by single-crystal X-ray diffraction. The structural results show that the bonding mode of 1 and the architecture of the resulting lattice is subtly influenced by the alkali metal and the presence of coordination or lattice solvation. The crystallisation of Na[1] from propan-2-ol/n-pentane produces an open clathrate-type structure of hexagonal type HS-I composed of fullerene-like units in which 1 behaves as a planar five-fold symmetric node with solvent-filled lattice voids. In contrast, crystallisation of the sodium, potassium, rubidium and caesium salts from the same solvent system results in highly condensed, unsolvated phases in which 1 adopts a variety of non-planar coordination modes involving four or five of the CN groups. When crystallised from nitromethane/diethyl ether, the potassium, rubidium and caesium complexes form solvated arrangements with coordinated MeNO₂ that contain helical subunits.

A series of dichlorocyclophosphazanes [{ClP(μ-NR)}₂] containing chiral and achiral R groups was obtained from simple commercially available amines and PCl₃. Their condensation reactions with axially chiral biaryl diols yielded ansa-bridged chiral cyclophosphazane (CycloP) ligands. This highly modular methodology allows extensive elaboration of the ligand set, in which the chirality can be introduced at the diol bridge and/or the amido R group. This provides the possibility to observe match and mismatch effects in catalysis. A series of twenty CycloP ligands was synthesized and characterized by multinuclear NMR spectroscopy, HRMS, elemental analysis, and in selected cases, single-crystal X-ray diffraction. These studies show that all of the ditopic CycloP ligands are C₂ symmetric, rendering their metal coordination sites symmetry equivalent. Two well-established enantioselective reactions were explored by using late-transition metal CycloP complexes as catalysts; the gold-catalyzed hydroamination of γ-allenyl sulfonamides and the asymmetric nickel-catalyzed three-component coupling of a diene and an aldehyde. The steric demands of the CycloP ligands have a subtle influence on the reactivity and selectivity observed in both reactions. Good enantiomeric ratios (e.r.) as high as 89:11 in the gold-catalyzed reaction and 92:8 in the nickel-catalyzed bis-homoallylation reaction were observed.

Deprotonation of [Et₃NH][C₅(CN)₅] with metal bases provides a very simple approach to coordination compounds containing the pentacyanocyclopentadienide anion [C₅(CN)₅]⁻ (1). The three-dimensional polymer [Na(thf)_1.5(1)]_∞ and the molecular dimer [{(tmeda)₂Na(1)}₂] are obtained by reaction of this precursor with NaH in the presence of thf or tmeda (Me₂NCH₂CH₂NMe₂). Their single-crystal X-ray structures both reveal σ-bonded CNNa arrangements and π stacking between [C₅(CN)₅]⁻ ions. DFT calculations on the [C₅(CN)₅]⁻ ion have been used to investigate the structures and bonding in [Na(thf)_1.5(1)]_∞ and [{(tmeda)₂Na(1)}₂]. The absence of π bonding of the metal ions in both complexes is due to dispersion of the negative charge from the C₅ ring unit to the CN groups in the [C₅(CN)₅]⁻ ion, making the coordination chemistry of this anion distinctly different from that of cyclopentadienide C₅H₅⁻.

The room-temperature reactions of Sn(NMe₂)₂ with less sterically demanding primary phosphines (RPH₂) give the homoleptic phosphanediide compounds [SnPR]_n in high yields (R=tBu (1 a), cyclohexyl (1 b), 1-adamantyl (1 c)). However, the room-temperature reaction of Mes*PH₂ (Mes*=2,4,6-tBu₃C₆H₂) with Sn(NMe₂)₂ gives the model intermediate [{SnPMes*}₂(μ-NMe₂)SnP(H)Mes*] (3), together with the product of complete deprotonation [SnPMes*]₃ (4). Phosphorusphosphorus bonded products are produced in these reactions at elevated temperatures. If the reaction producing 1 a is heated to reflux then [tBuP(H)P(H)tBu] is produced as the major product (together with tin metal). The novel octanuclear cage [{SnPtBu}₇Sn(PtBu)₃] (2) can also be isolated in low yield, resulting from formal addition of the heterocyclic stannylene [(tBuP)₃Sn] to a SnP single bond of the intact structure of 1 a. Prolonged heating of the reaction producing 3 and 4 leads to the formation of the diphosphene [PMes*]₂ (5) and tin metal. The X-ray structures of the heptamer 1 a (n=7), octanuclear 2 and trinuclear 3 are reported.